Depends on the tartan... Here's the trick I use:

Look at the tartan and squint your eyes. If there's a SINGLE LINE that really "jumps out" at you, the tartan will look good pleated to that line. If nothing really "pops", then it'll probably look better pleated to the sett.

All kilts look good pleated to the sett. SOME kilts look good pleated to the stripe.

My $.02